"He finally invited me over to this giant, extravagant house that he and Valerie had built before she split. It looked like vampires lived there," Hagar recalls. "There were bottles and cans all over the floor. The handle was broken off the refrigerator door. There were spider webs everywhere."

Adding to Hagar's horror, his pal "was sleeping on the floor with blanket and pillow. There was no food in the cupboard. I had never seen a dirtier place in my life. It was like the house out of that movie Grey Gardens. This was Eddie Van Halen, one of the sweetest guys I ever met. He had turned into the weirdest f*ck I'd ever seen: crude, rude and unkempt."

The hard-partying rock star had invited Hagar over to record new music for the group's reunion tour. Unfortunately, due to the mansion's dilapidated conditions, Eddie's plans never came to fruition.

"He had big blankets thrown over the windows. The mattresses were stripped off the beds and leaned against the wall for soundproofing. He was making music and trying to get the sound right," Hagar explains. "He had dug a trench to run wires from the studio to his house. We never used it even once for the three songs we eventually did record."

Though Hagar was tempted to pull out of the reunion tour after seeing his friend in such a disheveled state, "Eddie's got a very charming, cunning side to him, where you feel like he's got a good heart. He's going to come through. He's going to clean up and we're going to get this thing done."

Unfortunately, the condition of Eddie's home was an early indicator of what became the "craziest, most wacked-out" time in his career.

For more details on Hagar's final days in the band -- including how he attempted to stage an intervention for Eddie -- pick up the new issue of Rolling Stone, on stands now.